Slotted waveguide aerial system



July 15, 1969 M. J. CRUMPEN 3,456,261

SLOTTED WAVEGUIDE AERIAL SYSTEM Filed July 27, 1966 PR/oR ART INVENTOEMQW W TTOENEYJ United States Patent O U.S. Cl. 343-768 6 Claims ABSTRACTOF THE DISCLOSURE A slotted waveguide aerial system includes a length ofwaveguide having a narrow wall` slotted with in-phase slots on one sideof the middle of the length of guide and with anti-phase slots on theother side so that if the guide is fed at the centre point orco-phasially at its two ends the in-phase and anti-phase slots each havethe same main direction of beam radiation.

This invention relates to aerial systems and more specically to aerialsystems of the slotted waveguide type. Aerial systems of this type arein wide use for directional radio transmission and reception, one veryimportant use being in airborne Doppler navigation systems.

One of the diiculties encountered when a slotted waveguide directionalaerial is employed is that the main direction (the direction of theprincipal lobe in the polar radiation diagram) varies with frequency andif therefore the associated transmitter drifts in frequency there willbe a consequent undesired change in directivity. Temperature variationswill also cause undesired changes in directivity. It is customary tomeet these difficulties by constituting a slotted waveguide aerialsystem by two slotted waveguides, one an irl-phase guide and the otheran anti-phase guide, each fed at one end and suitably loaded at theother, the two guides being so arranged as to have a common maindirection. With such a two-guide system frequency drift and temperaturevariation effects in the two guides practically cancel out so far as themain direction is concerned so that this direction remains praeticallyconstant. However this expedient has the defect of being costly andresulting in a considerable increase in space and weight, because twoguides are required. The defects of bulkiness and weight areparticularly objectionable in the case of airborne equipments. Theobject of the present invention is to avoid these defects.

According to this invention a slotted waveguide aerial system comprisesa length of waveguide which is provided within-phase slotting on oneside of an intermediate point in said length and with anti-phaseslotting on the other side of said intermediate point, the slottingbeing such that if the guide is fed at said intermediate point or is fedcop'nasially at its two ends, the in-phase and antiphase slottingprovide a common main direction.

A preferred embodiment comprises a length of rectangularly sectionedwaveguide with one narrow wall slotted with in-phase slots on one sideof the middle of said length and with anti-phase slots on the other sidethereof.

In one arrangement the length of guide is provided with feeder means atsaid intermediate point and the outer ends of the guide length arereflectionlessly terminated eg. by suitably dimensioned terminatingresistances or by short circuiting diodes as known per se. Alternativelymeans may be provided for feeding the outer ends of the guide length inphase and the guide may be loaded at the intermediate point by asuitable resistance or diode. Obviously the common main direction willbe different when the guide is centre fed from what it is when the iceguide is end fed and where it is required to change over the common maindirection from one to the other (as will often be the case in anairborne Doppler navigation system) suitable waveguide switch mea-ns maybe provided for changing over from centre feed to end feed and viceversa.

The invention is illustrated in and further explained in connection withthe accompanying drawings in which:

FIGURE l shows a commonly employed known aerial system with two slottedguides, and

FIGURE 2 shows an embodiment of this invention.

Referring to FIGURE l, one waveguide 1 has in-phase slotting constitutedby a plurality of parallel radiating slots 2 in one narrow wall thereof,and the other waveguide 6 has anti-phase slotting constituted by twosets 7 and 8 each of parallel slots, those of set 7 alternating with andbeing oppositely inclined with respect to those of set 8 so that eachslot in one set is a mirror image of an adjacent slot in the other. Theguides are side by side and are fed at opposite ends 3 in the case ofguide 1 and 9 in the case of guide 6) in phase from a common source (notshown). The other ends of the guides are terminated by matched loads 4.The two waveguides, fed as described, will have a common direction ofprincipal radiation, indicated by the arrows 5 and 11 which will remainsubstantially unchanged by any variation of frequency or temperaturelikely to be encountered in practice. However the installation involvestwo guides and to that extent is costly, bulk and heavy.

The embodiment of this invention, shown in FIGURE 2, has only a singleguide 12. This guide has one narrow wall slotted with in-phase slots 13(the counterpart of the slots 2 of guide 1 of FIGURE 1) and anti-phaseslots 14 (the counterpart of the slots 7 and 8 of guide 6 of FIG- URE1). The in-phase slots are on one side of the middle of the guide `4 andthe anti-phase slots are on the other side thereof. As indicateddiagrammatically, a central feeder 15 is provided and the ends 16 and 17of the guide are terminated by matching loads 4. As indicated by theparallel arrows 18 and 19 there is a common principal direction forradiation from the two sets 13, 14 of slots. Alternatively the guidescould be fed in phase at their ends from a common source and terminatedby a matching load at the centre. This also results in a commonprincipal direction though, of course, it is different from thatindicated by the arrows 18 and 19 and is as indicated by the broken linearrows 18 and 19. If desired suitable switching means (not shown) may beprovided for changing over from centre feed to end feed and vice versaaud thus changing over from one common principal direction to the other.

I claim:

1. A slotted waveguide aerial system comprising a length of waveguidewhich is provided on one side of an intermediate point in said lengthwith a first plurality of slots which are arrayed along said length andare oriented in-phase with respect to one another, and is furtherprovided on the other side of said intermediate point with a secondplurality of slots which are arrayed along said length, some of saidsecond plurality of slots being oriented irl-phase with respect to oneanother and are oriented anti-phase with respect to others of saidsecond plurality of slots, the slotting being such that the in-phase andanti-phase slotting provides a common main direction when the guide isfed in one of the following ways, namely: (l) fed at said intermediatepoint, and (2) fed cophasially at its two ends.

2. An aerial system as claimed in claim 1 comprising a length ofrectangularly sectioned waveguide with one narrow wall slotted within-phase slots on one side of the middle of said length and withanti-phase slots on the other side thereof.

3. An aerial system as claimed in claim 1 wherein the length of guide isprovided with feeder means at said intermediate point and the outer endsof the guide length are reectionlessly terminated.

4. An aerial system as claimed in claim 1 wherein means are provided forfeeding the outer ends of the guide length in phase and the guide isloaded at the intermediate point.

5. A slotted waveguide aerial system comprising a length of waveguidewhich is provided on one side of an intermediate point in said lengthwith a first plurality of slots which are arrayed along said length andare oriented in-phase with respect to one another, and is furtherprovided on the other side of said intermediate point with a secondplurality of slots which are arrayed along said length, some of saidsecond plurality of slots being oriented in-phase with respect to oneanother and are oriented anti-phase with respect to others of saidsecond plurality of slots, the slotting being such that the in-phase andanti-phase slotting provides a common main direction when the guide isfed at said intermediate point.

6. A slotted waveguide aerial system comprising a length of waveguidewhich is provided on one side of an intermediate point in said lengthwith a first plurality of slots which are arrayed along said length andare oriented irl-phase with respect to one another, and is furtherprovided on the other side of said intermediate point with a secondplurality of slots which are arrayed along said length, some of saidsecond plurality of slots being oriented in-phase with respect to oneanother and are oriented anti-phase with respect to others of saidsecond plurality of slots, the slotting being such that the in-phase andanti-phase slotting provides a common main direction when the guide isfed cophasially at its two ends.

References Cited UNITED STATES PATENTS 3,293,645 12/1966 Farley et al.343770 HERMAN K. SAALBACH, Primary Examiner M. NUSSBAUM, AssistantExaminer U.S. Cl. XR.

